1. Field of the Invention
The present invention pertains to a flat belt pulley that securely clamps a flat belt to the pulley.
2. Description of the Related Art
High strength, limited stretch flat belts are often used in heavy load lifting and lowering applications. Examples of applications in which flat belts are used include belt and pulley drive systems that lift and lower heavy objects such as, elevator belt and pulley drive systems, fork lift belt and pulley drive systems and weight lifting apparatus belt and pulley drive systems. These types of flat belts are typically manufactured in open lengths with one end of the length being clamped to a drive pulley and the opposite end of the length being clamped to the object being lifted and lowered. The high strength and limited stretch properties of the flat belts are achieved by constructing the belts of a plurality of steel cords positioned side by side along the belt length. Each steel cord is constructed of multiple wound steel strands and the plurality of cords are encapsulated in a polyurethane resin.
The drive pulley to which one end of the flat belt is clamped is typically a flat-faced pulley with side flanges. The spacing between the side flanges is generally slightly larger than the width of the flat belt to ensure that the side flanges guide the flat belt and align each wrap of the flat belt on the pulley.
Flat belt pulleys are also designed with a special center hub that is constructed of two pieces with there being opposed, flat clamping surfaces on the two pieces of the hub. The two pieces of the hub include a large piece and a small piece, where the large piece includes the pulley shaft center bore. The small piece is clamped to the large piece with one end of the flat belt clamped between the opposed clamping surfaces of the two pieces of the hub.
In prior art clamping pulley constructions, the large piece and small piece of the pulley hub are typically clamped together by threaded fasteners. Fastener holes extend through the small piece of the pulley hub and align with internally threaded fastener holes in the large piece of the pulley hub. The fastener holes also extend through the opposed clamping surfaces of the pulley hub. It is therefore necessary that, when attaching one end of the flat belt to the pulley between the opposed clamping surfaces, holes must be provided through the end of the flat belt that align with the fastener holes in the pulley large piece and the fastener holes in the pulley small piece. Fasteners can then be inserted through the fastener holes in the pulley small piece, through the aligned holes provided in the belt end, and into the fastener holes of the pulley large piece. Tightening the fasteners then clamps the pulley small piece to the pulley large piece with the belt end positioned therebetween, thereby clamping the belt end to the pulley.
The need to provide fastener holes through the belt end being secured to the clamping pulley detracts from the strength of the flat belt by removing material from the end of the flat belt. Each fastener hole made through the end of the flat belt will at least remove some polyurethane from the end of the flat belt, and could also potentially cut through one or more of the steel cords reinforcing the end of the flat belt. Therefore, prior art flat belt clamping pulleys are disadvantaged in that they reduce the tensile strength of the end of the flat belt clamped to the pulley.